diff --git a/core/modules/settings_tray/js/settings_tray.es6.js b/core/modules/settings_tray/js/settings_tray.es6.js
index c182a873ed..a50f45198d 100644
--- a/core/modules/settings_tray/js/settings_tray.es6.js
+++ b/core/modules/settings_tray/js/settings_tray.es6.js
@@ -166,10 +166,10 @@
         }
 
         if (drupalSettings.hasOwnProperty('settings_tray') && drupalSettings.settings_tray.hasOwnProperty('overridden_blocks')) {
-          Object.entries(drupalSettings.settings_tray.overridden_blocks).forEach(
-            ([blockId, url]) => {
-              if (instance.options.url.includes(`/${blockId}/`)) {
-                instance.options.url = url;
+          Object.keys(drupalSettings.settings_tray.overridden_blocks).forEach(
+            (blockId) => {
+              if (instance.options.url.indexOf(`/admin/structure/block/manage/${blockId}/off-canvas`) !== -1) {
+                instance.options.url = drupalSettings.settings_tray.overridden_blocks[blockId];
               }
             },
           );
diff --git a/core/modules/settings_tray/js/settings_tray.js b/core/modules/settings_tray/js/settings_tray.js
index 98e81f3d93..9d7e80a1bf 100644
--- a/core/modules/settings_tray/js/settings_tray.js
+++ b/core/modules/settings_tray/js/settings_tray.js
@@ -4,7 +4,6 @@
 * https://www.drupal.org/node/2815083
 * @preserve
 **/
-var _slicedToArray = function () { function sliceIterator(arr, i) { var _arr = []; var _n = true; var _d = false; var _e = undefined; try { for (var _i = arr[Symbol.iterator](), _s; !(_n = (_s = _i.next()).done); _n = true) { _arr.push(_s.value); if (i && _arr.length === i) break; } } catch (err) { _d = true; _e = err; } finally { try { if (!_n && _i["return"]) _i["return"](); } finally { if (_d) throw _e; } } return _arr; } return function (arr, i) { if (Array.isArray(arr)) { return arr; } else if (Symbol.iterator in Object(arr)) { return sliceIterator(arr, i); } else { throw new TypeError("Invalid attempt to destructure non-iterable instance"); } }; }();
 
 (function ($, Drupal, drupalSettings) {
   var blockConfigureSelector = '[data-settings-tray-edit]';
@@ -103,13 +102,9 @@ var _slicedToArray = function () { function sliceIterator(arr, i) { var _arr = [
       }
 
       if (drupalSettings.hasOwnProperty('settings_tray') && drupalSettings.settings_tray.hasOwnProperty('overridden_blocks')) {
-        Object.entries(drupalSettings.settings_tray.overridden_blocks).forEach(function (_ref) {
-          var _ref2 = _slicedToArray(_ref, 2),
-              blockId = _ref2[0],
-              url = _ref2[1];
-
-          if (instance.options.url.includes('/' + blockId + '/')) {
-            instance.options.url = url;
+        Object.keys(drupalSettings.settings_tray.overridden_blocks).forEach(function (blockId) {
+          if (instance.options.url.indexOf('/admin/structure/block/manage/' + blockId + '/off-canvas') !== -1) {
+            instance.options.url = drupalSettings.settings_tray.overridden_blocks[blockId];
           }
         });
       }
diff --git a/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.info.yml b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.info.yml
new file mode 100644
index 0000000000..39fb56fa55
--- /dev/null
+++ b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.info.yml
@@ -0,0 +1,8 @@
+name: 'Configuration override test for Settings Tray'
+type: module
+package: Testing
+version: VERSION
+core: 8.x
+
+dependencies:
+  - settings_tray
diff --git a/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.services.yml b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.services.yml
new file mode 100644
index 0000000000..b23035bde2
--- /dev/null
+++ b/core/modules/settings_tray/tests/modules/settings_tray_override_test/settings_tray_override_test.services.yml
@@ -0,0 +1,5 @@
+services:
+  settings_tray_override_test.overrider:
+    class: Drupal\settings_tray_override_test\ConfigOverrider
+    tags:
+      - { name: config.factory.override}
diff --git a/core/modules/settings_tray/tests/modules/settings_tray_override_test/src/ConfigOverrider.php b/core/modules/settings_tray/tests/modules/settings_tray_override_test/src/ConfigOverrider.php
new file mode 100644
index 0000000000..1ee59631c5
--- /dev/null
+++ b/core/modules/settings_tray/tests/modules/settings_tray_override_test/src/ConfigOverrider.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace Drupal\settings_tray_override_test;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Config\ConfigFactoryOverrideInterface;
+use Drupal\Core\Config\StorageInterface;
+
+/**
+ * Provides an overridden block for Settings Tray testing.
+ *
+ * @see \Drupal\Tests\settings_tray\FunctionalJavascript\SettingsTrayBlockFormTest::testOverriddenDisabled()
+ */
+class ConfigOverrider implements ConfigFactoryOverrideInterface {
+
+
+  /**
+   * {@inheritdoc}
+   */
+  public function loadOverrides($names) {
+    $overrides = [];
+    if (TRUE || !empty($GLOBALS['config_test_run_module_overrides'])) {
+      if (in_array('block.block.overridden_block', $names)) {
+        $overrides = $overrides + ['block.block.overridden_block' => ['settings' => ['label' => 'ALL YOUR LABELS BELONG TO US']]];
+      }
+    }
+    return $overrides;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheSuffix() {
+    return 'ConfigOverrider';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function createConfigObject($name, $collection = StorageInterface::DEFAULT_COLLECTION) {
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheableMetadata($name) {
+    return new CacheableMetadata();
+  }
+
+}
diff --git a/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php b/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
index fcfecde400..5480fd512b 100644
--- a/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
+++ b/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\settings_tray\FunctionalJavascript;
 
+use Drupal\block\BlockInterface;
 use Drupal\block\Entity\Block;
 use Drupal\block_content\Entity\BlockContent;
 use Drupal\block_content\Entity\BlockContentType;
@@ -75,7 +76,7 @@ public function testBlocks($theme, $block_plugin, $new_page_text, $element_selec
     $page = $this->getSession()->getPage();
     $this->enableTheme($theme);
     $block = $this->placeBlock($block_plugin);
-    $block_selector = str_replace('_', '-', $this->getBlockSelector($block));
+    $block_selector = $this->getBlockCssSelector($block);
     $block_id = $block->id();
     $this->drupalGet('user');
 
@@ -267,8 +268,10 @@ protected function assertOffCanvasBlockFormIsValid() {
    * @param string $contextual_link_container
    *   The element that contains the contextual links. If none provide the
    *   $block_selector will be used.
+   * @param bool $confirm_form
+   *   Determines if the block form should be confirmed.
    */
-  protected function openBlockForm($block_selector, $contextual_link_container = '') {
+  protected function openBlockForm($block_selector, $contextual_link_container = '', $confirm_form = TRUE) {
     if (!$contextual_link_container) {
       $contextual_link_container = $block_selector;
     }
@@ -283,7 +286,10 @@ protected function openBlockForm($block_selector, $contextual_link_container = '
     $this->assertSession()->assertWaitOnAjaxRequest();
     $this->click($block_selector);
     $this->waitForOffCanvasToOpen();
-    $this->assertOffCanvasBlockFormIsValid();
+    if ($confirm_form) {
+      $this->assertOffCanvasBlockFormIsValid();
+    }
+
   }
 
   /**
@@ -321,7 +327,7 @@ public function testQuickEditLinks() {
       $this->enableTheme($theme);
 
       $block = $this->placeBlock($block_plugin);
-      $block_selector = str_replace('_', '-', $this->getBlockSelector($block));
+      $block_selector = $this->getBlockCssSelector($block);
       // Load the same page twice.
       foreach ([1, 2] as $page_load_times) {
         $this->drupalGet('node/' . $node->id());
@@ -577,4 +583,52 @@ protected function getTestThemes() {
     });
   }
 
+  /**
+   * Tests that the blocks with configuration overrides are disabled.
+   */
+  public function testOverriddenDisabled() {
+    $web_assert = $this->assertSession();
+    $overridden_text = 'This block cannot be edited in the Settings Tray form because it has configuration overrides in effect.';
+    $this->container->get('module_installer')->install(['settings_tray_override_test']);
+    // Test a overridden block does not show the form in the off-canvas dialog.
+    // @see \Drupal\settings_tray_override_test\ConfigOverrider
+    $overridden_block = $this->placeBlock('system_powered_by_block',
+      [
+        'id' => 'overridden_block',
+        'label_display' => 1,
+        'label' => 'This will be overridden.',
+      ]);
+    $this->drupalGet('user');
+    // Confirm the label is actually overridden.
+    $web_assert->elementContains('css', $this->getBlockCssSelector($overridden_block), 'ALL YOUR LABELS BELONG TO US');
+    $this->enableEditMode();
+    $this->openBlockForm($this->getBlockCssSelector($overridden_block), '', FALSE);
+    $web_assert->elementContains('css', self::OFF_CANVAS_CSS_SELECTOR, $overridden_text);
+
+    // Test a non-overridden block does show the form in the off-canvas dialog.
+    $block = $this->placeBlock('system_powered_by_block',
+      [
+        'label_display' => 1,
+        'label' => 'Labely label',
+      ]);
+    $this->drupalGet('user');
+    // Confirm the label is not overridden.
+    $web_assert->elementContains('css', $this->getBlockCssSelector($block), 'Labely label');
+    $this->openBlockForm($this->getBlockCssSelector($block));
+    $web_assert->elementNotContains('css', self::OFF_CANVAS_CSS_SELECTOR, $overridden_text);
+  }
+
+  /**
+   * Gets the CSS selector for a block.
+   *
+   * @param \Drupal\block\BlockInterface $block
+   *   The block.
+   *
+   * @return string
+   *   The CSS selector for the block.
+   */
+  protected function getBlockCssSelector(BlockInterface $block) {
+    return str_replace('_', '-', $this->getBlockSelector($block));
+  }
+
 }
diff --git a/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php b/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php
index d3f446cf6a..63d97badb9 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTestBase.php
@@ -9,6 +9,11 @@
  */
 abstract class OffCanvasTestBase extends JavascriptTestBase {
 
+  /**
+   * CSS select for the Off-canvas dialog.
+   */
+  const OFF_CANVAS_CSS_SELECTOR = '.ui-dialog[aria-describedby="drupal-off-canvas"]';
+
   /**
    * {@inheritdoc}
    */
@@ -83,7 +88,7 @@ protected function waitForOffCanvasToClose() {
    * @return \Behat\Mink\Element\NodeElement|null
    */
   protected function getOffCanvasDialog() {
-    $off_canvas_dialog = $this->getSession()->getPage()->find('css', '.ui-dialog[aria-describedby="drupal-off-canvas"]');
+    $off_canvas_dialog = $this->getSession()->getPage()->find('css', self::OFF_CANVAS_CSS_SELECTOR);
     $this->assertEquals(FALSE, empty($off_canvas_dialog), 'The off-canvas dialog was found.');
     return $off_canvas_dialog;
   }